Means to control cross talk



Sept. '15, 1925. I 5

' A. G. CHAPMAN ET AL I MEANS T0 CONTROL GROSS TALK 4 v INVENTORS J6:[ht 111mm WE GMCw dy ATTORNEY Patented Sept. 15 1925.

UNITED STATES 1,553,435 PATENT OFFICE. I

An'rnUE e. CHAPMAN, or EAST ORANGE, AND nAtrno. McCURDY, oar ENGLEWOOD,NEW JERSEY, ASSIGNOBS 'ro AMERICAN TELEPHONE Am) TELEGRAPH COMPANY,

A. CORPORATION OF NEW .YOBK.

'MEAns To common ,cnoss TALK.

Application filed December 9,- 1924; as-aim. 754,806.

Toallwlwmitmyconcem."

Be it known that-we, ARTHUR G. CHAP- MAN and RALPH G. MoCUnnY, residingat East Orange and Englewood, in the counties .of Essex .and Bergen andStates of "New Jersey and New Jersey, respectively, have. inventedcertain Improvements in Means to Control Cross Talk, of which thefollowing is a specification. f. y c

This invention relates to transmission circuits and more particularly toarrangements for reducing crosstalk or interference upon such circuits.

In designing cuits with respect to crosstalk hmitatlons there are twofactors to be taken into consideration, first, the effect of thecrosstalk v uplon the intelligibility of the conversation W the absenceof secrecy during gaps in the conversation. The latter factor determinesthe limiting condition for the reason that the maximum crosstalk currentwhich would be permissible without rendering the conversationunintelligible will'be greater than the maximum crosstalk which may bepermitted without rendering such crosstalk understandable during gaps inthe conversation.

It will be evident that if it were ossible to reduce or eliminate thecrosstal when conversation is not taking place over the circuit, lack ofsecrecy would not have to be. taken into consideration in designing thecircuits with respect to crosstalk and therefore a greater amount ofcrosstalk might be permitted (without rendering the circuitsuncommercial. In accordance with the present invention it is proposed toeliminate or reduce the crosstalk during such intervals as conversationis not taking place by roviding arrangements for normally disa ling thecircuitfor transmission' purposes, such disabling means being removed,however, under the control of voice currents when conversation takesplace.

The invention may now be more fully understood from the followingdescription when read in connection with the accompanying drawing, Fires 1, 2, 3 and 4 of which illustrate sc ematically four dif-' 4telephone transmission cirr .scriber. ile talking is taking place, and,second,

apparatus should be marginal so that it' will not respond to the maximumcrosstalk currents which may be permitted, but will readilyrespond toeven very weak v'oice currents transmitted from the sub- Referring toFig. 1, L designates a telephone transmission line of anywell knowntype, provided, if desired, with repeaters at suitable points along itslength. Near each terminal two-way repeaters R and R are provided. Therepeater R comprises a channel for transmitting cast, including anamplifier AE, and a channel for transmitting west, including anamplifier AW. The channel transmitting west includes voice operatedapparatus, comprising a rectifier 20 of well known type for convertingthe voice currents into direct current components and a voice operatedrelay 21 responsive to the rectified currents. The relay .21 isarranged, when energized, to open a short circuit 22, bridged across thewest transmission path of the repeater R. In order that the rela mayremove. the dis abling means as quick y as possible it should be sodesigned as to attract its armature very quickly. Consequently, as soonas the armature begins to move the short circuit will be opened and itwill not be necessary to take up the entire amount of time that has hadtime to open the short circuit,.a

delay circuit 23 may be included between the repeater AW and the shortcircuit 22. The relay 21 should be slow to release its armature so thatat the endof a s llable the short circuit 22 will not be close untilafter the latter part of the syllable has been transmitted through thedelay circuit. The repeater R is similar to the repeater R, comprisingan amplifier AE" in the path transmitting east and an am lifier AW inthe path transmitting west. ontrolling apparatus is provided inconnection with the path transmitting" west, said controlling apparatuscomprising rectifier quick acting and slow-release relay 21', a shortcircuit 22' ggntrolled by'the relay, and a delay circuit tion with therepeater R.

Both the relays 21 and 21"are marginal in their action so that they willnot respond to .the maximum crosstalk currents which may be permittedwithout renderin conversation unintelligible, but will respond to thesmall est Voice currents transmitted over the circuit from thesubscribers stations. It will also be noted that the short circuit 22nor- *m ally disables the circuit for transmission from east to west,while the short circuit 22' normally disables the circuit for transmis-fsion from west toeast.

If the east subscriber should begin talking, the currents will 'betransmitted through the amplifier AW over line L andthrough theamplifier AW. The crest of: the wave entering the circuit, including therectifier 20 operates the marginal rela 21 to-open' the short circuit22, the delay circuit 23 peri I mitting this operation to takeplacebefore the crest of the wave reaches the point at which the shortcircuit'22 is applied. The voice currents then pass on to the westsubscriber. If the west subscriber should begin talking the currentswill be transmitted through the amplifier AE, over the line L,andthrough the amplifier AE', thus actuati'ng therelay 21 to remove theshort circuit 22, permitting the currents to'pass on to the eastsubscriber. During gaps in the conversation the circuit is disabled fortrans mission in either direction by means of the short circuit 22 nearthe west terminal of the line, which revents transmission fromeast towest, and y means of the short circuit 22' near the east terminal oftheline, which prevents transmission in the opposite direction. Crosstalkcurrents arising along the line L between the-terminals cannot betransmitted beyond the short circuited points-and hence cannot be heardby the subscribers during the gaps in the conversation. Loss of'se:crecy will accordingly be prevented.

Where the circuit is not provided with repeaters the voice-opera edcontrolling means maybe applied near th terminals, as illustrated inFig. 2, instead of being applied at terminal repeater points, as in Fig.1, The

disabling arrangement near the west terminal comprises a short circuit22, controlled by either of two marginal relays 21 or 25.

These elements function in a manner similar to those already describedin connec- The relay 21 is controlled rectified voice currentssuppliedby a recti er 20, which is and the point at which the shortcircuit 22 occurs. A similar arrangement is provided at the eastterminal of the line;

Under normal conditions when no conversation is taking place the line Lis short circuited near each terminal by the short circuits 22 and 22respectively. If the east subscriber begins to talk to the westsubscriber voice currents rectified by the rectifier 20 operate theslow-release relay 21 to open the short circuit 22'. The delay circuit23 prevents the crest of the voice wave from arriving at the shortcircuited point until this operation takes place. Upon opening the shortcircuit the voice currents pass through the delay circuit 26' and onover the line L to. the distant terminal. The voice currents arriving atthe west terminal are rectified by the rectifier 20 and operate therelay 21 to open a short circuit 22. The delay circuit 23 permits thisoperation to take place before the voice currents arrive at the point atwhich the short circuit is applied. As soon as the short circuit isopened the voice currents pass on through the delay circuit 26 .to thewest, subscriber. If'the west subscriber talks to the east subscriber,the operation will be reversed, the relays25 and 25',being operated toopen the short circuits 22 and 22';

In this case, as in the case previously described, the relays 21, 21, 25and 25 must be constructed'to operate upon very narrow margins so thatthey will not respond to the maximum crosstalk currents but will respondto the weakest voice currents transmitted by, the subscribers.

A modified arrangement is illustrated in F ig. 3, which enables the useof repeaters which are not provided with balancing arrangements at theterminal repeater points. A single amplifying element A is providedwhich may be switched to transmit either east or west in a manner to bedescribed. A rectifier 20 is bridged across the line L near the point atwhich it enters the'repeaterlR for the purpose of supplying rectifiedcurrents to the marginal relay 21. Similarly, a rectifier 24 is bridgedacross the west termi- ,nalfor supplying rectified currents to themarginal relay 25.

B elay 21, when energized, performs three flmctions: First, it connectsthe input side of the amplifer A to the west terminal of the line L;second, it connects" the outputside ofthe amplifier A to the subscribersline going west, and, third, it opens the bridge a circuit including therectifier 24 and the relay 25.- Similarly, the relay 25, when energized,connects the input circuit of the amplifier A to the subscribers line-West,

connects the output circuit of the amplifier the west subscriberbeg insto talk, however,

the relay 25 will be operated'to switch the amplifier'A into the circuitin a direction to transmit'from west to east, at the same time 25disabling the rectifier 20. The delay circuit 26 permits the switchingoperation to take place before the crest of the voice wave istransmitted through the delay circuit and arrives at the switching pointcontrolled by 30 the relay 25.

ously described, the various marginal relays.

must be designed so thatthey will not respond to the maximum crosstalkcurrents 4 which are permissible without causing unin-.

telligibility, at the same time being readily responsive to the weakestcurrents transmitted by subscribers conversing over the line. Fig. 4shows an arrangement similar to that of Fig. 3 except that the terminalrepeaters are each provided with two amplifiers, one for transmittingeast and one for transmitting west. For example, the repeater Risprovided with an amplifier AE, the input of which is normallyconnected to the line leading to the west subscriber and the output ofwhich is normally disconnected from the -line L, The repeater is alsoprovided with an amplifier AW, the input of'which is normally connectedto the line L, and the output of which is normally disconnected from theline-leading to thewest subscriber. A rectifier 20 and marginal relay 21are'bridged across the output side of the amplifier AW and when operatedserve to disconnect the input of the repeater AE from the line leadingto the west subscriber' A similar operation takes place in connectionwith the relay 25' ofthe and to connectthe output of the amplifier AWto'the line leading to the west 'sub- J scriben A delay circuit 22 enablesthe switching operation to take place before the crest of the voice wavearrives at the switching point. Similarly, a rectifier 24 and marginalrela T 25 are bridged across the output side of t e amplifier AE, theseelements, when operated, functioning to disconnect the input-'side'ofthe amplifier AW from the line L and to connect the output side of theamplifier AE to said line; [The delay circuit 26 permits this switchingoperationtotake place before the voice currents arrive at the switchingpoint. The apparatusat re eater R'- is similar to that already describeNormally, the circuit is disabled'fortrans -mission either direction byreasonof the fact that the output circuit-of each of the amplifiers isopen-circuited. Consequently, duringperiods when no conversation is tak-I ing place, crosstalk currents arising at any point, along the'line Lbetween the repeater stations-cannot be transmitted '-to the sub--scribers. If-the West subscriber commences to talk,'the marginal relay25 will be oper ated to switch the line L to the. output side of theamplifier AB. The voice currents may then pass through the amplifier AEand the delay circuit 26 tot'he' line L. Upon arrivin at the repeater Rthe-marginal relay 25 operates to connect the line going to theeast-subscriber with the output circuit of the amplifier AE Similarly,if the east subscriber commences to talk, relays 21' and21 will operateto connect the output sidesof amplifiers AW. and AW to theeast terminalof the line L and to the line going to the west subscriber respectively,so that the voice currents maybe transmitted from "end vto end in thedirection from east to west. Here, again, the relays performing theswitching operations must be marginal to -prevent being responsive tocrosstalk currents while readily responding to west sigcurrentstransmitted by the subhone' as defined line interconnecting twosubscribers stations, meanslto normally prevent transmission from saidline to either subscribers sta-. tion, and means responsive to voicecurrents originating at a subscribers station for permittingtransmission from said subscrlbers station over the line to the-othersubscribers station,said means being unresponsiye. to crosstalk currentsinduced, in the line, 2. In a transmisslonlsystem, a telephone.

line interconnecting two subscribers" stations, meansassociated withsaid l me near the station terminals thereof to normally 'preventtransmission from the line to "the tions, switching means normallyrendering said line inoperative for transmission to either station, andmeans responsive to voice I currents "for controlling. said switchingmeans, said means being unresponsive to crosstalk currents induced inthe line.

4. In a transmission system, a telephone line interconnecting twosubscribers Sta tions, switching means normally rendering said lineinoperative for transmission to either station, and means responsive tovoice currents transmitted from one of said sta tions to control saidswitchlng means so as I to enable transmission from said station oversaid line to the other station, said last'me'n-' tioned means beingunresponsive to crosstalk currents induced in the line.

- 5. In a transmission system, a telephon line interconnecting twosubscribers stations, switching means near one station terminal of theline for disabling the line for transmission from the line to thatstation, means responsive to voice currents transmitted over the line ina direction towards-said station for controlling said switching means topermit transmission'in 7 that direction,

said means being unresponsive to crosstalk said line for preventingtransmission from said line to the other terminal station, and

means responsive to voice currents transmitted over the line in adirection towards said other station for-controlling said last mentionedswitching means topermit transmission ov'erthe line to said otherstation, said means being unresponsive to crosstalk '.'currents inducedin the line.

6. In a transmission system, a telephone line interconnecting twosubscribers statlons, two-way repeaters associated with said line neareach station terminal thereof, means normally disabling one of saidrepeaters for transmission in-one direction, means for normallydisabling the other repeater forv transmission in the oppositedirection, and means responsive to voice currentsoriginating at eitherstation for controlling said disabling means to permit transmissionbetween stations, said-:means being unresponsive to crosstalk currentsinduced in the line. v

7. In a transmission system, a telephone l ne interconnecting two'subscribers stations, means normally disabling said line fortransmission during intervals when voice currents are not present, andmeans responsive to voice currents transmitted from one of said stationsto enable transmission to take place over said line, ,said lastmentioned means being unresponsive to crosstalk currents induced in theline.

In testimony whereof, we have signed our names to this specificationDecember 1924.

'ARTHUR G. CHAPMAN. RALPH G. MoCURDY.

this "8th day of

